Answer:
When we round to the nearest hundred, we must look at the tens digit.
If the tens digit is 5 or lager, then we round up (we add 1 to the hundreds digit and after that, all the digits are zero.)
If the tens digit is smaller than 5, then we round down (the hundreds digit remains unchanged and after that, we complete with zeros.)
Then, the rounded number is 1900.
a) The greatest whole number that rounds to 1900 would be a number that is rounded down, then it will be:
1949
b) The least whole number that is rounded to 1900 is a number that we round up, this is:
1850